Can closure

ABSTRACT

Cans sealed with removable pressure-sensitive adhesive tape tabs over a pour hole successfully contain carbonated beverages or other pressure-generating liquids if the area around the pour hole and under the tape is slightly elevated, thereby putting the tape in shear rather in peel. Circular can ends may be provided with a circular pour hole, taped and then shaped to impart a frusto-conical area around the pour hole before being crimped over the tubular can body.

"United States Patent [191 Viker et al.

[ June 17, 1975 CAN CLOSURE [75] inventors: Harris W. Viker, Roseville;William E. Kropp, North St. Paul, both of Minn.

[73] Assignees Minnesota Mining and Manufacturing Company, St. Paul,Minn. 1

22 Filed: Aug. 30, 1973 21 Appl.N0.:393,001

52 u.s.c| 220/359; 229/7 R; 222/541 [51] Int. Cl B6511 41/00 [58] Fieldof Search 220/53, 47, 48, 27, 359;

[56] 8 References Cited UNITED STATES PATENTS Paal 229/7 R 3,441,1674/1969 Balocca 220/53 Primary Examiner--Ge0rge T. Hall 1 Attorney,Agent, or Firm-Alexander, Sell, Steldt DeLaHunt v [57 ABSTRACT Canssealed with removable pressure-sensitive adhesive tape tabs over a pourhole successfully contain carbonated beverages or otherpressure-generating liquids if the area around the pour hole and underthe tape is slightly elevated, thereby putting the tape inshear ratherin peel. Circular can ends may be pro vided with a circular pour hole,taped and then shaped to impart a frusto-conical area around the pourhole before being crimped over the tubular can body.

6 Claims, 3 Drawing Figures CAN CLOSURE BACKGROUND'OF THE INVENTION Thisinvention relates to liquid-containing cans of the type in which a pourhole is covered by a removable pressure-sensitive adhesive tape tab. Theinvention also relates to end walls useful for the manufacture of suchcans and to methods of preparing such end walls.

Over the past several years there has been an increasing use of metalcontainers for carbonated soft drinks and beer. These containers areopened by lifting and more economical, carbonated beverage manufactureslater resorted to fabricating the tubular side wall and one end wallfrom steel, using openable aluminum for only the other end wall. In somecases an aluminum insert, including a tear strip was incorporated into asteel can end. Although such dual metal cans are satisfactory for theintended use, it is ecologically desirable today for empty cans to becapable of simple recycling; the separation of the aluminum from steelis both inconvenient and expensive. Additionally, several states andcities have banned the use of ring pull cans because the removed tabsareso commonly dropped on the ground or thrown into a body of water, wherethey decompose only very slowly.

It is known that unpressurized cans containing tomato juice and similarliquids can be provided with a convenient means for opening bypre-punching a hole in one end wall and applying a pressure-sensitiveadhesive tape, tab over the hole. When the user desires to open such acontainer, he grasps the free end of the tape tab and pulls the closureoff, exposing the hole in the end wall to permit pouring out thecontents of the can. Easy-open containers of this type are shown in U.S.Pat. No. 3,389,827, the disclosure of which is incorporated herein byreference.

Various attempts have been made to adapt the seal ing technology of theaforementioned patent to the packaging of gas-containing liquids such ascarbonated soft drinks and beer, but these attempts have not provedcommercially satisfactory. Typical pressures for various beverages at38C. are as follows: orange 1.7 .17 kg/cm strong beer, 3.3 kg/cm rootbeer, ginger ale, cola and lemon, 4.5 kg/cm club soda, 5.8 kg/cm At roomtemperature (21C.), pressures are about 70%, and even under normalrefrigeration (e.g., 45C.), they are about 40%, of the values justcited. Such pressures bulge prior art tape closures upward and graduallypeel them from the area immediately circumjacent to the pour hole, and,in a relatively short time, break the seals. Prior to the present time,then, it has been felt that tape closures could not be employed in thesealing of highly pressurized containers.

SUMMARY The present invention provides a closed liquid-filled hollowcontainer which is economical to manufacture, utilizes the simple andeasily operated pressuresensitive adhesive tab of the type shown in US.Pat. No. 3,389,827, can be fabricated entirely from steel,

and resists high internal pressures for an extended period of time.

In accordance with the invention, the area of the can wall immediatelycircumjacent to the pour hole is so contoured that it tapers outward,and the hole is thus located in a plane displaced outward with respectto the rest of the end wall. When the can is filled with apressure-generating liquid, the portion of the tape covering the holebulges outward, as in previous constructions. Because of the contour ofthe can wall circumjacent to the hole, however, the forces acting on thetape tend to place the adhesive in shear (i.e., the forces are exertedparallel to the tape backing) instead of in peel (i.e., where the forcesare exerted at right angles to the tape backing). Since the shear forcerequired to loosen the tape greatly exceeds the peel force required toloosen it, the container can be subjected to substantially higherinternal pressure without seal failure than is possible when the hole islocated in the same plane as the remainder of the wall.

In fabricating containers of the invention, it has been found convenientto employ a subassembly comprising a preformed circular end piece whichis a modification of the conventional type, having a depressed centerend wall with a died-out pour hole and a circumferential lip forclamping over and sealing to one end of tubular metal can body. Themodification is conveniently made by applying to the depressed centerportion of the end piece a strip of normally tacky andpressure-sensitive adhesive tape so that it overlies the pour hole andis sealed to the circumjacent surface, supporting the taped side of theend piece in an area adjacent to but spaced slightly outward from thepour hole, and firmly gripping the end piece in this area. The area ofthe end wall immediately circumjacent to the pour hole is then taperedoutward by forcing a blunt punch into the pour hole from the side of theend piece which has not been taped. Where the pour hole is circular, thepunch normally will have a head with a circular cross section in a planetaken at right angles to the axis of the punch. The distal end of thehead then has a diameter smaller than that of the pour hole and theremainder of the head has a diameter larger than that of the pour hole;the head may be beveled, tapered, chamfered, or curved in order toachieve this shape. As the head is forced into the pour hole, it impartsan open-topped outwardly tapered configuration to the taped side of theend piece, simultaneously stretching the tape and leaving it firmlyadhered.

BRIEF DESCRIPTION OF THE DRAWING Understanding of the invention will befurther facilitated by reference to the accompanying drawing, in whichlike numbers refers to like parts in the several views and in which:

FIG. 1 is a perspective view of a can made in accordance with thepresent invention;

FIG. 2 is a cross section of the end wall of the can shown in FIG. 1,taken along section line 2-2 and looking in the direction of the arrows;and

FIG. 3 is a cross sectional view of a forming press suitable forimparting a frusto-conical configuration to the end wall ofa can in thearea immediately circumjacent to the pour hole.

DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS In evaluating theeffectiveness of can end walls made in accordance with the invention toresist pressure, it has been found convenient to employ a water-tightchamber equipped with an electric heating element'and having temperaturecontrols in the base. The chamber is provided with a top having several68.3-mm holes designed to accommodate can lids for pressure testing. Alid hinged to the chamber contains several 68.3-mm holes correspondingto those in the top of the chamber. Can end walls to be tested aremounted over the holes in the top, after which the cover is bolted tothe chamber. To perform a test, the water is heated to the desired testtemperature, the desired air pressure supplied to the base of thechamber, and an electric timer mounted above each test lid started; thetimer is connected to a pressure-activated switch, which in turn isconnected to the lid. The switch is closed, and the timer therebystopped, when the tape closure is sufficiently loosened to permit escapeof the pressure in the chamber, thus marking the end of the test.

In the drawings, can comprises generally circular upper end and tubularbody 30. (Can 10, of course, has a generally circular lower end which isnot visible). End 20 comprises a circumferential lip 21, having a resincoating 22 at its inner aspect; lip 21 fits down over the upper end ofcan body 30 and is crimped in position, resin 22 sealing the jointagainst leakage. The central portion of end wall 23 is depressedslightly with respect to lip 21, a common arrangement in canmanufacture. Located in end wall 23 adjacent lip 21 is pour hole 25,which, if circular, typically has a diameter of 10-15 mm; slightlyradially inward therefrom is located vent hole 24, which typically has adiameter of 1 /2 3 mm. In the area 26 circumjacent to pour hole 25, endwall 23 is so contoured that it tapers upward, leaving pour holesituated in a plane spaced slightly (e.g., 2-4 mm) above the remainderof end wall 23. To minimize damage, especially in stacking or handling,pour hole 25 is preferably located in a plane which is slightly lowerthan the upper portion of lip 21. The difference in elevation betweenthe pour hole 25 and can end wall 23 in the formed end 20 should usuallybe, for a 12.7- mm pour hole, on the order of 2 /2 3 mm, and the angleof the sides to the base should generally exceed 20 to insure placingthe tape closure in a shear mode adequate to resist failure underanticipated conditions of use.

Overlying pour hole 25 and vent hole 24 is sealing tab 40, theconstruction of which is shown best in the crosssectional view of FIG.2. Tab 40 comprises stretchable backing 41, advantageously formed of astrong oriented synthetic polymeric film which is 25-250 microns thick,although metal foil or reinforced fibrous sheet material can probably beemployed in some circumstances. It is important, however, that thebacking of the sealing tab be relatively impermeable to water vapor,carbon dioxide and oxygen. Water vapor transmission, for example, shouldnot exceed 1.7-1.8 gms/IOO in /24 hr/mil at 23C. when measured inaccordance with ASTM Test E96. Carbon dioxide should have a permeabilityrate which does not exceed 15-25 cc/l00 in /24 hr/atmosphere at 25C.,and oxygen permeability should not exceed about -40% of this figure; seeASTM Test D 1434. It is also important for the film to be capable ofelongating lO-200% at break so that the tab can be stretched to conformto the convex area around the pour hole. To insure continued smoothconformance, the stretched backing should not, after withdrawing thestretching force, retract more than 30% of the incremental amountstretched; in fact, a backing which possesses dead stretch (i.e., noretraction) is preferred.

In order to minimize any difference in appearance between tab 40 and endwall 23, it is often desirable to impart a metallic appearance tosealing tab 40; this can be accomplished by laminating a metal foil or athin transparent polymeric film, aluminum vapor coated on its lowersurface, over the top of backing 41. If desired, backing 41 may beprovided with a thin coating of vapor-deposited aluminum on its exposedsurface. Coated over the lower surface of backing 41 is a layer offirmly adherently bonded normally tacky and pressure-sensitive adhesive32. The distal end of tab 40 is made easier to grasp initially bycovering a portion of the adhesive with a small piece of film or paper.The nature of the adhesive layer should be such that the force requiredto peel it from steel (U.S. Federal Standard No, 147) should be in therange of 0.9-2.8 kg/cm width to insure adequate adhesion and yet permitremoval of the tab with a reasonable amount of effort. The backing must,of course, be strong enough not to tear during removal.

In order to minimize corrosion of the raw edge of end wall 23 whichimmediately surrounds vent hole 24 and pour hole 25, it is generallypreferred to apply a light coating of a protective polymeric material 27after sealing tab 40 has been adhered in place; this protective coatingalso covers the exposed surface of pressuresensitive adhesive 42,obviating any possibility that the can contents may be contaminated withundesirable flavors leached from the adhesive. In carrying out thepressure test described above, it has been found that more consistentresults are obtained if coating 27 is eliminated; in the actualpackaging of carbonated liquids, however, coating 27 is normallyincluded.

Turning now to FIG. 3, the method of forming can end 20 in-accordancewith the invention will be discussed. Vent hole 24 and pour hole 25 aredie-cut from the end wall 23 of an end 20, sealing tab 40 appliedthereover, and a protective coating 27 of lacquer or the like applied toprotect the raw edges. End 20 is then inverted and placed atop acircular support table 50, the diameter of which is the same as thediameter of end wall 23. In the upper surface of table 50 is a generallycylindrical cavity 51, the diameter of which is somewhat greater thanthe diameter of pour hole 25. Can end 20 is so positioned that pour hole25 is centered over cavity 51.

Connected to table 50 by means of supporting member 52 is press head 60,coil springs 53 surrounding member 52 to maintain the press in normallyopen position. Punch 61, at the lower end of which is chamfered head 62,is seated in press head 60. The location of head 62 may be controlled bythe insertion of shims (not shown) between the lower surface of presshead 60 and the upper surface of head 62. Suspended somewhat below thelower surface of press head 60 is forming ring 63, supported by threeguide pins 64, only one of which is shown in the drawing. Guide pin 64slides in channel 65, spring 66 surrounding the exposed portion of guidepin 64 and holding forming ring 63 a fixed distance beneath the lowersurface of press body 60. Positioned in axially aligned relationshipwith respect to punch 61 is hole 67, the diameter of which is slightlygreater than the greatest diameter of head 62.

After can end is positioned on the upper surface of table 50, press head60 is lowered, bringing draw ring 63 into snug contact with end wall 23everywhere except in the portion of end wall 23 immediately circumjacentto pour hole 25. As head 60 is further lowered, punch head 62 contactsthe portion of end wall I 23 which defines pour hole 25 and graduallyforces it into a frusto-conical shape, the configuration of which isdictated by the angle, a, of the chamfered portion of head 62. v

In many situations it may be preferable to employ a pour hole which isother than circular, e.g., an elliptical hole which takes the place ofboth pour hole 25 and vent hole 24. The same principles of tapering thearea circumjacent such a hole apply, but the resultant shape is not afrustum in the strict geometric sense. As used herein, however, theterms frustum, frustoconical, etc., are intended to be liberallyconstrued so as to embrace such shapes. Similarly, where the termdiameter is employed, it is not intendedthat a circular cross-section isnecessarily connoted thereby.

For some purposes, pour hole 25 need not be a single large hole but maybe a plurality of closely spaced smaller holes. In this event, all theholes should be located in the plane which is spaced farthest from theupper surface of end wall 23. Likewise, although holes which have theshape of a circle or regular polygon are simple and economical,teardrop, oval, or other shapes may be employed. Where the hole isnon-circular, however, it is desirable to use tape which has deadstretch, or at least very little elastic memory.

Understanding of the invention will be further facilitated by referenceto the following illustrative but nonlimiting examples, in which allparts are by weight unless otherwise noted.

EXAMPLE 1 Biaxially oriented polyethylene terephthalate filmapproximately 90 microns thick was provided on one face with a thinvapor coating of aluminum to impart a metallic appearance. The oppositeface was then coated with a thin primer layer of astyrene-butadiene-styrene block copolymer in which each of the twopolystyrene blocks had a molecular weight of about 15,000 and thepolybutadiene block had a molecular weight of about 70,000. (A suitablecopolymer of this type is available from Shell Chemical Company underthe registered trademark Kraton 1101.) The coating was then exposed to acorona discharge to bond it firmly to the film backing. Over the primedface was applied a tolu' ene solution containing 100 parts of the sameblock copolymer and 95 parts of a polyterpene resin containingalpha-pinene and having a ring-and-ball softening point (ASTMM TestE28-58T) of 135C. (A suitable polyterpene resin is available fromPennsylvania Industrial Chemical Corporation under the registeredtrademark designation Piccolyte 62135.) The coated solution was thenoven dried to leave a pressure-sensitive adhesive coating weighingapproximately 6 rngmlcm The sheet material was then wound into rollform, a silicone-coated paper release liner being interposed betweenadjacent convolutions in the roll.

From the linered pressure-sensitive sheet material described in thepreceding paragraph a tab similar in shape to tab 40 in FIG. 1 was died.The overall length of the tab was just over 50 mm, the distal grippingportion being 25 mm wide and 10 mm deep, the central portion 12 /2 mmwide X 18 mm long, and the circular end 22 mm in diameter. A strip ofpaper was then applied to the pressure-sensitive adhesive coating of thegripping portion.

A conventional 68.3-mm diameter depressed-center beverage can end waspunched as shown in FIG. 1 so that it had a pour hole approximately 9.5mm in diameter and a vent hole approximately 1.6 mm in diameter. Overthe outer surface of the can end was then applied the tab described inthe preceding paragraph, the resulting laminate being subjected to apressure of approximately 40 kg/cm at 50C. (Adhesion may be furtherincreased by utilizing higher temperatures, higher pressures, or both.For many end uses, however, application may be made at room temperatureand pressures as low as 6 kg/cm Over the lower surface of the can lid,in the areas immediately adjacent to the edges of the pour hole and thevent hole, was applied a 25% toluene solution of a protectiverubber-resin coating. The solid material consisted of parts of the blockcopolymer used in the primer coating (described earlier in this example)and parts of a non-oxidizing white hydrocarbon copolymer of 65% mandp-vinyl toluene and 35% alpha-methyl styrene. (A suitable hydrocarboncopolymer of this type, having an ASTM E28-5 8T ball-and-ring softeningpoint of 92C., is available from Pennsylvania Industrial ChemicalCorporation under the registered trademark Piccotex LC.) The solvent wasevaporated and the taped, edge-sealed can end placed in a 65C. oven for4 hours to enhance adhesion of the tab; longer times, highertemperatures, or both, improve adhesion still more.

The taped lid, prepared as just described, was shaped on an apparatussimilar to that shown in FIG. 3, as described earlier, so as to impact afrustum-like configuration to the pour hole and the immediatelysurrounding area. The pour hole opening was enlarged to a diameter ofabout 11 mm, and the height of the frustum was about 2.2 mm above theremaining area of the can end. The sides of the frustum lay at an angleof about 30 to the remainder of the can lid, the base blending into thecan end in a smooth curve.

When the sealed lid was mounted on the end of a can containingpressurized liquid, it functioned extremely effectively but could beremoved easily.

Tabulated below are examples showing the effect of several variables onthe performance of products made in accordance with the invention. Noneof these examples included a protective edge sealing coat; otherwise,all are made in substantially the same way as Example 1.

For convenience, the following abbreviations are employed in the table:

PET Biaxially oriented polytli'ylelifi terephthalate film IPP Biaxiallyoriented isataetie ally pro lene film -Continued Elastomeric film of23:48:28 acrylonitrile:styrene:butyl acrylate polymer. having a densityof 1.07 and a melt index at 200C./21.6 kgf of 8-12 g/mm, per ASTM TestNo. 1238. Resin of this type is available from BASF under the tradedesignation Luran, and film is sold by Richman Chemical Company asRichform ASA. Adhesive blend of 100 parts of the block copolymer ofExample 1 and 90 parts of a-pinene resin having a ball-and-ringsoftening point of 135C, coated from 40% solution in toluene Adhesiveblend of 100 parts crude rubber smoked sheets, 19 partsphenol-formaldehyde resin, 19 parts wood rosin and 65 partspoly-B-terpene. Adhesive based on vinyl acetatezZ-ethylhexylacrylatezvinyl alcoholzacrylic acid polymer (e.g., available fromMonsanto under the registered trademark Gelva" MP-276), crosslinked withpolycarbodiimide Adhesive based on 27:19:51z3 vinyl acetate: ethylacrylate:2ethylhexyl acrylatezacrylic acid polymer (e.g., available fromAshland Chemical Company under the registered trademark Aeroset" 1044),crosslinked with p-toluene sulfonic acid-catalyzed melamine resin ASASBS

Crude VOAC:2EHA:- VAzEA 0 ant, albeit strong, sealing tab; thus,although a 90 slope is theoretically ideal, it is generally quiteimpractical to attain.

It is not feasible to provide an exhaustive list of the variouscomponents, which might be employed in practicing the invention. It hasbeen demonstrated, however, that various polymeric films and laminatescan be used as backings for the closures, and that any primer must takeaccount of both the backing and the subsequently applied adhesive.Although normally tacky and pressure-sensitive adhesives possess manyadvantages,

IOAIEAIAA 50140110 -Q Y P W Y hot melt adhesives, especially those whichbecome acrylatezacrylic acid terpolymer k h h d d k f PolyamidePolyamide resin havinga ball-and-ring softening tac y w en edte an remamtac y some tlm e P 2 1 2f g g g g of gl thereafter, are also useful.Presumably highly elastic at .an cm at- .,an a ore hardness (ASTM Test D1707431) of 85 thermoset resins could also be employed. available fromGeneral Mills under the It will likewise be appreciated that while thema or ig trademark desgnaton Versalo" utility of structures formed inaccordance with the in- PEPU Highly crystalline thermoplastic polyestervention resides in the packaging of pressure-generating PO Yurethane 'fliquid, such structures also find application in the packstate, has atack retention of 2 hours, stress-strain values are 64 kg/cm at 3O agingof particulate or non-pressure generating liquid 2 clmigmon "P 9 kg/cm.700% material, the slightly elevated area surrounding the (Suitableresins, disclosed in U.S. Patent No. 237L213, are available f B11Goodrich pour hole facilitating removal of the contents in a simunderthe registered trademark Estane 5712) 1 d Convenient manner SPE Solublepolyester formed by coreacting f isophthalic acid, terephthalic acid andethylene What is claimed 15 as Onowsglycol 1. In a closed hollowcontainer wherein a pour hole Examples 21O Film Backing EffectivenessThickness, Test Pressure Time to Example Composition microns PrimerAdhesive Temp.C. kg/cm fail, min.*

Control PET 90 SPE S85 38 3.5 4,332 2 H H H .H H H 10,000 Control 5.2525-30 3 H H H H H H L400 Control 6.3 9-12 4 H H H H H H H2 Control PET,aluminum 50 lOA:EA:AA, 38 3.5

vapor-coated peroxide crosslinked 5 H H H H H H 18] Control lPP AtacticCrude 2-3 polypropylene 6 H H H H H H 31 1 Control Polyamide 43 15.7 7 HH H H H H 986 Control VOAC12EHA 2.5 8 [PF 50 VOACZZEHA 43 3.5 12.0Control VA:EA:2EHA:AA 4.4 9 H H H H H H 153 Control ASA Polyamide PEPU2.8 76.5 10 H H H H H H L820 Test ended after 10,000 minutes. whether ornot failure had occurred.

Those skilled in the art will readily recognize that practice of theinvention is susceptible of many variations without departure from thespirit of what has been disclosed. For example, the dimensions recitedare not intended to be narrowly applied. It has been found, however,that it is preferable for the slope of the tapered area to be linearrather than either concave or in the container wall is protectivelycovered by a tape removably adhered to the outer surface of the wall inthe area immediately circumjacent to the pour hole,

the improvement which comprises contouring said area so that the walluniformly tapers outward and the hole is thus located in a planedisplaced outward with respect to the portion of the wall peripherallyadjoining said area, the tape being adhered to the'tapered portion ofthe wall,

whereby, without causing the tape to loosen, the container can besubjected to substantially higher internal pressure than is possiblewhen the hole is located in the same plane as the immediatelycircumjacent area.

2. The invention of claim 1 wherein the container is a cylindrical metalcan having circular ends, the pour hole being located in one of saidends.

3. The invention of claim 2 wherein said one end is recessed, the heightof the tapered area not exceeding the distance said one end is recessed.

4. The invention of claim 3 wherein the can contains a carbonatedbeverage.

5. The invention of claim 3 wherein the shape of the tapered area isthat of a frustum.

6. A subassembly for use in fabricating the can of claim 2, comprising apre-formed circular end piece having a depressed center end wall and acircumferential lip for clamping over and sealing to one end of anannular metal can body, said end wall having a portion which isdisplaced upward therefrom, a pour hole being located at the top of theupwardly displaced portion, with a strip of tape protectively coveringsaid pour hole and sealed to the upwardly displaced side of the end wallin the area immediately circumjacent to the pour hole.

1. In a closed hollow container wherein a pour hole in the containerwall is protectively covered by a tape removably adhered to the outersurface of the wall in the area immediately circumjacent to the pourhole, the improvement which comprises contouring said area so that thewall uniformly tapers outward and the hole is thus located in a planedisplaced outward with respect to the portion of the wall peripherallyadjoining said area, the tape being adhered to the tapered portion ofthe wall, whereby, without causing the tape to loosen, the container canbe subjected to substantially higher inteRnal pressure than is possiblewhen the hole is located in the same plane as the immediatelycircumjacent area.
 2. The invention of claim 1 wherein the container isa cylindrical metal can having circular ends, the pour hole beinglocated in one of said ends.
 3. The invention of claim 2 wherein saidone end is recessed, the height of the tapered area not exceeding thedistance said one end is recessed.
 4. The invention of claim 3 whereinthe can contains a carbonated beverage.
 5. The invention of claim 3wherein the shape of the tapered area is that of a frustum.
 6. Asubassembly for use in fabricating the can of claim 2, comprising apre-formed circular end piece having a depressed center end wall and acircumferential lip for clamping over and sealing to one end of anannular metal can body, said end wall having a portion which isdisplaced upward therefrom, a pour hole being located at the top of theupwardly displaced portion, with a strip of tape protectively coveringsaid pour hole and sealed to the upwardly displaced side of the end wallin the area immediately circumjacent to the pour hole.